At the beginning of 1939, German chemist O. Hahn and physical chemist F. Strassman published papers on nuclear fission of uranium atoms. Within a few weeks, scientists from many countries verified this discovery and further suggested that it was possible to create conditions for this fission reaction to proceed on its own, thus opening up a broad prospect of using this new energy to create wealth for mankind. However, like many new scientific and technological discoveries in history, the development of nuclear energy was first used for military purposes, that is, to make a powerful atomic bomb, and its process was influenced and restricted by social and political conditions at that time.
Since 1939, it has become increasingly difficult for many European countries to carry out scientific research due to the expansion of the fascist German war of aggression. At the beginning of September of the same year, Danish physicist N.H.D Bohr and his collaborator J.A. Wheeler theoretically expounded the process of nuclear fission reaction, and pointed out that the best element that can cause this reaction is the isotope uranium 235. At the same time that this enlightening research result was published, Britain and France declared war on Germany.
/kloc-in the summer of 0/940, the Germans occupied France. Some scientists, led by French physicist Joliot-Curie, were forced to emigrate. Britain had made plans to carry out research in this field, but due to the war, manpower and material resources were in short supply. Later, it had to cooperate with the United States and send a team of scientists headed by physicist chadwick to the United States to participate in the development of the atomic bomb led by theoretical physicist Oppenheimer.
In the United States, the Hungarian physicist Zilad Leo, who moved from Europe, first considered that once fascist Germany mastered the atomic bomb technology, it might bring serious consequences. After he and several other scientists who immigrated to the United States from Europe rushed to promote it,1In August, 939, physicist A. Einstein wrote to the 32nd President of the United States, F. D. Roosevelt, suggesting the development of an atomic bomb, which attracted the attention of the American government. However, at the beginning, only $6,000 was allocated. It was not until the Japanese attacked Pearl Harbor in February that 194 1 expanded its scale. By August, 1942 had developed into a huge project code-named "Manhattan Project Area", which directly employed about 600,000 people and invested more than 2 billion US dollars. By the end of World War II, three atomic bombs had been built, making the United States the first country to have an atomic bomb.
To make an atomic bomb, we must not only solve a series of scientific and technical problems in weapon development, but also produce two necessary nuclear charges, uranium 235 and plutonium 239. The abundance of isotope uranium 235 in natural uranium is only 0.72%, which must be increased to more than 90% according to the design requirements of atomic bombs. At that time, after various explorations, studies and comparisons, the United States adopted three methods to produce this highly enriched uranium: electromagnetic separation, gas diffusion and thermal diffusion. Dozens of kilograms of highly enriched uranium used in the "marksmanship" atomic bomb are produced by electromagnetic separation. The cost of building an electromagnetic separation plant is about 300 million dollars (the conductive coil of the magnet is made of silver borrowed from the state treasury, and its value has not been included). Plutonium -239 is produced by neutron irradiation of uranium -238 in the reactor. Dozens of kilograms of plutonium -239 used in two "implosion" atomic bombs are produced by three graphite moderated water-cooled natural uranium reactors and their supporting chemical separation plants. The above example can illustrate the scale of the project at that time. Because America's industrial and technological facilities and construction are not directly threatened by war, and it has mastered the necessary resources and concentrated a group of domestic and foreign scientific and technological talents, so that it can quickly realize its atomic bomb development plan.
German technology was in the leading position at that time. Before 1942, Germany's level in the field of nuclear technology was roughly equal to that of the United States and Britain, and then it fell behind. The first experimental graphite reactor in the United States, led by physicist E. Fermi, was completed in194265438+February and reached the critical point; In Germany, however, heavy water reactors were used to produce plutonium-239, and a small subcritical device was not built until the beginning of 1945. In order to produce highly enriched uranium, Germany once focused on developing high-speed centrifuges, but due to air strikes and lack of electricity and materials, the progress was very slow. A. Hitler's persecution of scientists and the uncooperative attitude of some scientists are another reason for the slow progress in this field. More importantly, German fascist leaders are too confident that the war will be over soon, and they don't need to work hard to develop an uncertain atomic bomb. At first, they refused to support it, then it was difficult to grasp it, and the development work finally failed.
1945 After the German surrender in May, many people in the United States knew the inside story of "Manhattan Project Area", including a large number of scientists engaged in this work headed by physicist J. Franck, who opposed bombing Japanese cities with atomic bombs. At that time, the Japanese invaders were severely hit by China's long-term War of Resistance against Japanese Aggression, and their strength was greatly weakened. The attack of the United States and Britain in the Pacific almost wiped out the Japanese navy, and the sea blockade made Japan's domestic material supply extremely scarce. With Japan's defeat a foregone conclusion, the United States dropped two atomic bombs on Hiroshima and Nagasaki, Japan, only on August 6 and 9.
Before the German invasion in June, the Soviet Union was also committed to developing atomic bombs. The spontaneous fission of uranium nucleus was discovered by Soviet physicists гн flerov and κ а Petzak during this period. After the outbreak of the Great Patriotic War, the research work was interrupted until the beginning of 1943, when it was gradually resumed under the leadership of physicist kurchatov, and it was accelerated after the war. 1949 In August, the Soviet Union conducted an atomic bomb test. 1950 65438+ 10, U.S. President H.S. Truman ordered the accelerated development of hydrogen bombs. 1952, 165438+ 10, the principle test of hydrogen bomb with liquid deuterium as thermonuclear fuel was carried out in the United States, but the experimental device was very bulky and could not be used as a weapon. 1In August, 953, the Soviet Union conducted a hydrogen bomb test with solid lithium deuteride 6 as thermonuclear fuel, which made it possible to put the hydrogen bomb into practical use. The United States conducted a similar hydrogen bomb test in February 1954. Britain and France also conducted atomic and hydrogen bomb tests in the 1950s and 1960s.
When China began to build socialism in an all-round way, the basic industry developed to a certain extent, that is, it began to prepare for the development of the atomic bomb. 1959 started with serious difficulties in the national economy. 1In June 1959, the Soviet government tore up the "New Defense Technology Agreement" signed by China and the Soviet Union in June 1957, and then withdrew the experts. China is determined to complete this task entirely on its own. The code name of China's first atomic bomb was 596, which inspired China's military and civilians to do this work together. 1964 10 10/6, the first atomic bomb test was successful. After more than two years,19665438+February 28th, the principle test of small equivalent hydrogen bomb was successful. Half a year later, in June 1967 and 17, the airdrop test of the million-ton hydrogen bomb was successful. Adhering to the principle of independence and self-reliance, China has completed the tasks of these two stages of nuclear weapons development at the fastest speed in the world.